Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $84.89   13.326%   $96.2024   $96.20   $96.20   $96.20  
  Purchase #2 $119.32   10.131%   $131.4083   $131.41   $131.40   $131.40  
  Purchase #3 $120.88   11.318%   $134.5612   $134.56   $134.55   $134.60  
  Purchase #4 $111.98   4.259%   $116.7492   $116.75   $116.75   $116.70  
  Purchase #5 $217.57   11.121%   $241.766   $241.77   $241.75   $241.80  
  Purchase #6 $207.55   5.741%   $219.4654   $219.47   $219.45   $219.50  
  Purchase #7 $159.71   9.612%   $175.0613   $175.06   $175.05   $175.10  
  7 purchase totals = $1,021.90       $1,115.2138   $1,115.22   $1,115.15   $1,115.30